Year	Number
1999	23.00966
2000	23.32075
2001	23.10667
2003	22.96309
2004	19.01282
2005	16.29268
2006	15.01818
2007	14.08511
2008	14.07045
2009	13.85049
2010	14.16243
2011	13.97191
2012	13.91624
2013	14.78078
2014	15.26244
2015	14.95617
2016	16.25357
2017	15.05443
2018	15.07994